A308710 Primitive practical numbers of the form 2^i * prime(k).

6, 20, 28, 88, 104, 272, 304, 368, 464, 496, 1184, 1312, 1376, 1504, 1696, 1888, 1952, 4288, 4544, 4672, 5056, 5312, 5696, 6208, 6464, 6592, 6848, 6976, 7232, 8128, 16768, 17536, 17792, 19072, 19328, 20096, 20864, 21376, 22144, 22912, 23168, 24448, 24704, 25216

Offset: 1

Author

Miko Labalan, Jun 19 2019

Keywords

• nonn

Comments

Intersection of A267124 and A100368.

a(n) is a number of the form 2^i * prime(k) for i > 0 and A007053(i) < k <= A007053(i+1).

Terms are pseudoperfect numbers, A005835 and are also primitive pseudoperfect numbers, A006036.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040, A000079, A005153, A005835, A006036, A007053, A100368, A267124.

Programs

Mathematica

a[n_] := (p = Prime[n+1]) * 2^Floor[Log2[p]]; Array[a, 50] (* Amiram Eldar, Sep 22 2019 *)

PARI

isok(n) = is_A100368(n) && is_A267124(n); \\ Michel Marcus, Jun 19 2019

Formula

a(n) = 2^floor(log_2(prime(n+1))) * prime(n+1).